The present invention relates to footwear and in particular to a boot that is constructed to protect the foot of a wearer from serious damage resulting from the impact of a projectile and/or explosions from anti-personnel mines inadvertently detonated by the boot wearer. The present invention is also directed to a material that can be used, in one application, in the footwear described in the present application.
Anti-personnel mines which are designed to explode as a person steps on or near the mine represent a common and serious problem for any troops deployed either on a conventional battle field or involved in guerilla warfare.
The amount of explosive present in a mine will dictate whether the mine on exploding maims or kills the person triggering the mine. For those devices designed simply to maim, protective footwear can play a role in lessening the likelihood of serious injury. Such footwear can also have a role in lessening the damage caused by the impact of projectiles such as bullets and shrapnel.
The present inventor has developed boots, and in particular boot soles, that can afford a level of protection to the foot of a person triggering an anti-personnel mine containing reasonable quantities of explosive while still providing the wearer with sufficient toe-to-heel flexion in the boot to allow activities such as running, jumping and climbing (see International Application Nos PCT/SG96/00001, PCT/SG96/00008 and PCT/SG97/00010).
The present invention is directed to a new type of boot structure that offers an improved level of protection to wearers that may inadvertently trigger an anti-personnel mine.
According to a first aspect, the present invention comprises a sole for an article of footwear, the sole including at least one corrugated layer of a substantially blast and/or fragment resistant material.
In one embodiment, the corrugated layer is only present in the heel of the sole. In another embodiment, the corrugated layer can be present in the portion of the sole extending forwardly from the heel or the fore portion. In a still further embodiment, the corrugated layer can extend across a substantial portion of or the entire sole. The corrugated layer is preferably formed in the sole such that the corrugations extend transversely to the longitudinal axis of the sole. In a further preferred embodiment, each of the corrugations are preferably at about a right angle to the longitudinal axis of the sole.
The corrugated layer can be formed in the sole with a planar layer formed from the blast and/or fragment resistant material disposed on the upper and/or lower sides of the corrugated layer. Preferably, the planar layer can be disposed on the upper and/or lower sides of the corrugated layer such that it meets the peaks of some or each of the corrugations of the corrugated layer. The planar layer on the upper and/or lower sides of the corrugated layer, can be formed integrally with the corrugated layer or brought into fixed attachment with the corrugated layer. Where a planar layer is disposed on at least one of the upper or lower sides of the corrugated layer, at least a first set of a plurality of channels are formed in the sole. The present inventor has determined that these channels are surprisingly effective in channelling blast gases, generated when a mine is triggered, laterally away from the foot of the wearer.
In one embodiment of the invention, the sole can have at least one corrugated layer in both the heel and the fore portion extending forwardly from the heel, with the respective corrugated layers in the heel and fore portions being formed from different materials.
The corrugated layer and planar layers disposed on the upper or lower sides of the corrugated layer can be formed from a metal-matrix composite material. The composite can be formed from woven or chopped graphite, a ceramic material or a combination of such materials. In a preferred embodiment, it is formed from woven graphite (ie carbon fibre) of the type 3K TOW, 380 g/m2, M60/T300 that has been impregnated with a polymer containing a metal powder. The polymer can comprise either a polymer solution or molten polymer, with the metal being a metal alloy. The metal alloy can constitute at least 20% w/w of the polymer. Examples of the metal powder include aluminium alloys, such as an alloy of aluminium, nickel and molybdenum.
To form the composite, the woven graphite can be passed through a drier (such as an electric furnace) and then through a bath of molten alloy which fully wets the fabric. In a preferred embodiment, the molten alloy is a molten aluminium alloy of aluminium, nickel and molybdenum. As the woven graphite passes through the molten alloy, the polymer carburises between 500xc2x0 C. and 600xc2x0 C. and a chemical bond is created between the graphite fibres and the metal. The metal matrix composite is then passed through a set of rollers that are capable of exerting about 35 to 40 tons of compressive force and which squeeze out all excess metal alloy from the composite. The result is a composite material impregnated with metal.
The metal powder added to the polymer impregnating the woven graphite can also include titanium and nickel alloys. In this case, up to 50% w/w of the metal powder can be added to the molten polymer. By using such metal powders, the step of passing the impregnated woven graphite through the bath of molten alloy can be discarded. Instead, the woven graphite can be simply passed through the drier and then through the rollers.
Other metals, such as titanium, beryllium and metal alloys of various types can then be applied to the material to provide excellent bonding of the material. The other metals can also be applied by processes such as plasma spraying or hot sheet pressing.
In an alternative embodiment, the corrugated layer and planar layers disposed on the upper and/or lower sides of the corrugated layer can be formed from a polymer impregnated or an epoxy resin impregnated composite.
In a preferred embodiment of the invention, the sole includes a heel plate including a first upper portion of one or more, and preferably three, layers of woven aramid fibre. The woven aramid layers can each be formed from 280 g/m2 woven aramid. During the manufacturing process for the sole, the layers of woven aramid fibre are preferably held together by a porous coat of adhesive, such as hot melt polyurethane adhesive. In the heel plate, the corrugated layer preferably does not extend outwardly to the periphery of the first upper portion of one or more layers of woven aramid fibre. Rather, it preferably extends to a position inwardly from the periphery with the distance or gap between the periphery of the inner portion and the corrugated layer being substantially identical about the periphery of the heel plate. In one particularly preferred embodiment, the distance between the periphery of the first upper portion and the periphery of the corrugated layer is about 7 mm. As an example only, the material forming the corrugated layer in the heel portion can have a thickness of about 0.38 mm, with the corrugations having a height of about 4.5 mm and a peak to peak spacing of about 2 mm.
In a further embodiment, the sole includes a flexible fore plate disposed in the fore portion of the sole. The fore plate preferably includes a first upper portion of one or more, and preferably three, layers of woven aramid fibre. Again, the woven aramid layers can each be formed from 280 g/m2 woven aramid. During the manufacturing process for the sole, the layers of woven aramid in the first upper portion of the fore plate are also preferably held together by a porous coat of adhesive, such as hot melt polyurethane adhesive.
In the case of the fore plate, the corrugated layer is preferably positioned in the fore plate immediately below the first upper portion and comprises a layer of corrugated polymer impregnated composite. The corrugated layer preferably does not extend to the periphery of the first upper portion of one or more layers of woven aramid fibre. Rather, it preferably extends to a position inwardly from the periphery with the distance or gap between the periphery of the first upper portion and the periphery of the corrugated layer being substantially identical about the periphery of the fore plate. In one particularly preferred embodiment, the distance between the periphery of the first upper portion and the periphery of the corrugated layer is about 7 mm. The polymer impregnated composite can comprise two layers of woven aramid and, more preferably, two layers of 280 g/m2 scoured Twaron. To form this composite, the woven fabric is impregnated with a polymer solution. The fabric is then preferably passed through a drier, and then through a bath of molten nylon which wets the fabric completely. Ultrasonic vibrators can be used to vibrate the molten nylon as the fabric is passed therethrough. The composite is then passed between two rollers that exert at least several tons of compression on the fabric to squeeze out excess polymer from the composite. It is preferred that the resulting polymer impregnated composite contains less than 30% w/w of polymer.
The corrugated impregnated polymer composite layer in the fore plate is preferably adhered with epoxy resin to the first upper portion of one or more layers of woven aramid. In addition, the composite layer can be stitched to the first upper portion. As an example only, the material forming the corrugated layer in the fore plate can have a wall thickness of about 0.4 mm, with the corrugations having a height of about 4.5 mm and a peak to peak spacing of about 2 m.
The sole according to the present invention is adapted to be part of an article of footwear, such as a boot worn by infantry troops in combat zones.
According to a second aspect, the present invention comprises a blast-resistant sole for an article of footwear adapted to offer a level of protection to the foot of the wearer of the footwear if the wearer inadvertently triggers an explosive device, the sole having a longitudinal axis and including a plurality of channels extending transversely to the longitudinal axis, each of the channels being adapted to channel blast gases, generated when the explosive device is triggered, laterally away from the foot of the wearer.
In this second aspect, the plurality of channels can be formed by the provision of at least one corrugated layer of blast-resistant material as described herein.
In each of the above aspects, the boot preferably further includes a cocoon of substantially blast-resistant material that is incorporated into the boot. The cocoon is preferably adapted to substantially or entirely surround the foot of a wearer of the boot. The cocoon can be integrated within the upper of the boot or comprise the upper. In a preferred embodiment, the upper is preferably formed from a natural or synthetic leather outer layer and an inner vamp layer of leather or cotton between which the cocoon is positioned. The cocoon is preferably formed from one or more layers of blast-resistant material. In one embodiment, the cocoon can include at least two layers of woven aramid. The woven aramid can be 450 g/m2 ZyPhir material made for ZyPhir Research by Akzo-Nobel Twaron. The layers of woven aramid of the cocoon can also be stitched together with aramid fibre (such as ZyPhir 210 thread) to form an integrated protective and supportive cocoon. The layers of woven aramid are also preferably bonded with polyurethane hot melt adhesive that is applied as a porous coating. The result preferably is a material for the cocoon that is water-resistant yet breathable. In a specific application, a soft and pliable polyurethane hot melt is applied as a coating between the at least two layers of aramid. The polyurethane hot melt can be applied in a layer of about 0.05 mm. This embodiment of the boot has particular application in cold climates but could be used in warmer conditions.
In another embodiment, the cocoon can comprise a sandwich of layers of woven ceramic fibres or woven ceramic/glass-ceramic composite fibres and aramid fibres.
The sole according to the present invention is preferably stitched about its periphery to the cocoon. Where there is a distance or gap between the periphery of the corrugated layer and the periphery of the inner portion, the stitching between the sole and the cocoon preferably is made outside the periphery of the corrugated layer.
The sole according to the present invention preferably also includes an additional layer of blast-resistant material disposed between the lower surface of the cocoon and the at least one corrugated blast-resistant layer included in the sole. The additional layer is preferably comprised of a plurality of layers of woven aramid fibre. In a particularly preferred embodiment, the additional layer can comprise at least fifteen layers of woven aramid fibre. The woven aramid fibre can comprise 200 g/m2 ZyPhir material that is made for ZyPhir Research by Akzo-Nobel Twaron. Preferably, each layer of woven aramid is bonded together with a fine spray of hot melt polyurethane adhesive. The polyurethane adhesive is preferably applied as a porous coating of about 5g of polyurethane per square metre of woven aramid.
The sole according to the present invention preferably includes a still further layer of blast-resistant material disposed between the additional layer and the at least one corrugated blast-resistant layer included in the sole. The still further layer can be formed from at least one layer of woven aramid and at least one layer of woven ceramic fibre. It is particularly preferred that a woven ceramic fibre layer is the outermost or bottommost layer of the still further layer of blast-resistant material. It is further preferred that the still further layer includes a plurality of layers of woven aramid and woven ceramic fibre, with the aramid and ceramic fibre layers being layered in alternating sequence. Again, it is preferred that the ceramic fibre layer be the outermost or bottommost layer of the still further layer. In one embodiment, as an example only, the still further layer can include two layers of woven aramid fibre interleaved with two layers of woven ceramic fibre, again with one of the woven ceramic layers being the outermost or bottommost layer. The woven aramid fibre can be formed from 280 g/m2 aramid in this example. In still other embodiments, some or each of the layers of woven ceramic fibre can be replaced with woven ceramic/glass-ceramic composite fibres.
The sole preferably includes an outermost ground-engaging layer. This layer is preferably formed from rubber or polyurethanie. In the case of the rubber sole it can be vulcanised onto the boot. The ground-engaging layer can be formed in at least two layers, an outermost layer and an inner layer. The outermost layer can comprise a nitrile rubber and the inner layer can be formed of a foam rubber. The nitrile rubber can have a specific gravity of 1.6 and a Shore A hardness of 85. The nitrile rubber layer can be about 3 mm. The foam rubber layer can have a specific gravity of 0.6 and a Shore A hardness of 40. The foam rubber layer provides a greater level of comfort to the wearer of the footwear than if the outermost layer was formed entirely of nitrile rubber as described.